The purpose of this investigation is to improve the management of patients with suspected deep vein thrombosis and/or pulmonary embolism through improved combinations of noninvasive diagnostic techniques. The study is designed to prospectively assess patients with suspected venous thromboembolism in order to: 1) Determine the relative accuracy of several noninvasive or minimally invasive screening tests of venous thrombosis (Doppler ultrasound, plethysmography, I-125 fibrinogen scans, and radionuclide phlebography) and pulmonary embolism (perfusion and ventilation lung scans and leg vein screening) compared to the diagnostic standards of contrast phlebography and pulmonary arteriography. 2) Correlate I-125 fibrinogen scans and radionuclide phlebograms in detection of active venous thrombosis and defining true recurrent deep vein thrombosis. 3) Determine the incidence of detectable venous thrombosis in patients with proven pulmonary embolism. 4) Assess the incidence and prophylaxis of thrombotic complications of contrast phlebography and pulmonary arteriography. 5) Define the course of abnormal I-125 fibrinogen scans during anticoagulation for venous thrombosis. The goal of this research will be to define the most appropriate combination of objective diagnostic screening tests to overcome the limitations of the clinical diagnosis and the risk of invasive studies of clinical venous thromboembolism.